Photoshop

From Seamonster

Introduction

We collect a lot of digital photographs in this project. There are many applications available to edit these images and the most complex and powerful of the lot is called Photoshop. This page proves some notes about using Photoshop, in particular aligning a time sequence of images that might be taken from slightly different camera perspectives. These notes are courtesy of one of our interns (Erica).

Using Photoshop To Align A Time Sequence of Images

Let's assume one has 20 images taken from roughly the same perspective of an interesting event. If the camera is tripod-mounted then coregistering them is hopefully quite simple because they already are... but if the camera is hand-held, say one is taking photos of a whale breaching and the camera has a 5-fps mode, then each image must be coregistered with a master frame in order to eliminate jerkiness in a synthetic short movie. There are many methods to do this but one is to simply line everything up in photoshop and print the aligned frames one at a time to jpeg or png or whatever format.

Introduction

Photoshop is not difficult to use but neither is it completely intuitive. The main idea we use here is that each new image is imported to a unique layer and the layers are activated and made visible using a Layer toolbox that usually starts out at the lower right side of the application window. The terms I use here (Layer Tool, Draw Tool) I just made up; Photoshop probably uses different terms.

Open Photoshop
File menu: Open the reference photo
Layer menu: Create a new layer
...Use icon on the Layers Tool or Layer menu: Create
...Eye-icon by each layer determines if it is visible.
...Highlighted (blue background) layers are said to be selected.
File menu: Place allows you to put a second image on this new layer
...To complete the Place action hit Enter
...Now we have two images on two separate layers
Layers Tool: Change the Opacity value to view the 2nd layer as a ghost over the first
Keep the original photo at 100% Opacity.
Don't mess with Fill, a different type of opacity feature.
The plan from here is:
...Warp the second image to match the first
...Create a duplicate image (not layer!) which will be used to generate a jpeg file
...In the Duplicate: Hide the reference image so that only the second image is visible.
...Make the second image 100% opaque
...Save As... (a jpeg if convenient, many formats available)
...Can choose 50% grey matte to put a neutral background on uncovered regions
...Delete this Duplicate image and repeat for all images to be coregistered
Draw Tool (tall-and-thin, many iconified tools (lasso, mag, pointer, hand) starts at left
...Draw Tool has 3 Display Mode icons towards the bottom
...1. Standard screen mode: A bit inconvenient
...2. Fullscreen mode with menu bar: Most desirable (permits image manipulation).
...3. Fullscreen mode without menu bar (at top) so no File menu etcetera.
Draw Tool: At top right (arrow + 4-arrowheads) icon is Translate Current Active Layer tool
...Arrow keys will nudge the Active Layer image
Draw Tool: Mag glass zooms in/out.
Can zoom in and coregister to a pixel if desired
Ctrl + and Ctrl - zooms in and out
Draw Tool Hand icon: Activate to move all layers as one
Draw Tool Hand icon: Double click to restore normal centered view
Note in Edit menu: the Free Transform is the default
...This could be used to warp and otherwise munge the active layer image
To rotate a layer:
...Make sure it is selected (with no sub-selections)
...Edit menu: Transform: Rotate
...Move cursor outside of the frame box to get a curved rotate cursor, drag to rotate
Other warp/shift/etc transformations ought to be be investigated as well
Don't know if there is a tiepoint warp
Any camera will produce geometric distortion across the fov.

Example of results

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Photoshop

From Seamonster

Introduction

Using Photoshop To Align A Time Sequence of Images

Introduction

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